This application claims the benefit of Japanese Application No.10-339759 which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates generally to a full-color projection type display device having such a construction that reflection type light valves for R-, G- and B-light beams are disposed, beams of polarized light in individual colors which enter the respective light bulbs are modulated and exit, the modulated beams of light assuming the respective colors from the light valves are synthesized of colors, an analyzing optical system analyzes and takes out the synthesized beams of light, and the analyzed beams of light are projected through a projection lens, and more particularly to a projection type display device capable of reducing a projection of a ghost image.
2. Related Background Art
What is known as a prior art projection type display device is a full-color projection type display device disclosed in, e.g., Japanese Patent Application Publication No.2505758.
FIG. 18 shows the projection type display device disclosed in FIG. 1 of the above Patent Application Publication, and this display device will hereinafter be briefly explained.
Light beams emitted from a light source 23 travel through a shaping lens 22, then are converted into. substantially collimated beams of light and enter a polarization beam splitter 21. The light source beams entering the polarization beam splitter 21 are separated in polarization into beams of S-polarized light reflected by a polarization separator of the polarization beam splitter, and beams of P-polarized light penetrating through this polarization separator. The former beams of S-polarized light exit from the polarization beam splitter 21 and enter a color separating/synthesizing composite prism constructed of prisms 11A, 11B, 11C. Note that in this color separating/synthesizing composite prism, a surface 11e of the prism 11A is formed with a B-light reflection dichroic film, and a bonded surface between the prisms 11B and 11C is formed with an R-light reflection dichroic film. Further, an air gap is formed between the prisms 11A and 11B.
The light beams entering the prism 11A from the surface 11a travel through the prism, then impinge upon the B-light reflection dichroic film formed on the surface 11e, and are separated of colors into beams of B-light reflected therefrom and mixed beams of R- and G-light penetrating through the B-light reflection dichroic film, entering the prism 11B and traveling therethrough. The beams of B-light reflected by this film travel through the prism 11A, then are totally reflected by the surface 11a, further travel and exit from an outgoing surface 11b. Subsequently, the beams of B-light enter a B-light oriented reflection light valve 12 disposed in the vicinity of the outgoing surface. On the other hand, the mixed beams of R- and G-light having penetrated therethrough are incident upon the R-light reflection dichroic film. The beams of R-light reflected from this film travel through the prism 11B, then are totally reflected by an incident surface of the prism 11B, subsequently exit from an outgoing surface 11C and enter the R-light oriented light valve 13. The beams of G-light having traveled through the prism 11C travel further as they are, then exit from a surface 11d, and enter the G-light oriented light valve 14.
The beams of S-polarized light entering the respective color light oriented light valves receive modulating action by color signals and are thereby converted into beams of P-polarized light. Then, the light beams are reflected and exit as mixed beams of light of the thus modulated P-polarized light defined as the modulated light and the S-polarized light defined as the non-modulated light. The mixed beams of light exiting from the respective color light oriented light valves travel back along the above light paths, and exit as the color-synthesized beams of light from the surface 11a of the prism 11A. The color-synthesized beams of light are again made incident upon the polarization beam splitter 21, whereby only the P-polarized light as the modulated light is analyzed and taken out as the light of transmission through the polarization beam splitter. The color-synthesized light beams which have been analyzed enter the projection lens 24, thereby forming a desired full-color projected image on a screen 25.
In the projection type display device described above, however, it has proven that there might be a case where a ghost image is formed on the screen.
What has hitherto been known as a method of preventing the ghost image from appearing in the projected image on the projection type display device using the reflection type light valves may be a method disclosed in Japanese Patent Application Laid-Open Publication No.5-93887. A quarter-wave phase plate is disposed on the light path between the polarization beam splitter and the projection lens, the light beams among the projected beams of light entering the projection lens, which are reflected from the surfaces of some lens elements constituting the projection lens and travel back, are again incident on the light valves and reflected therefrom, and the ghost image is formed when these reflected beams of light reenter the projection lens. The above method was contrived to prevent this ghost image from being thus formed. Namely, the light beams conceived as a cause of the ghost image pass through the quarter-wave phase plate twice, thereby changing oscillating directions of the polarization thereof. With this being utilized, the light beams of the cause are cast away by the polarization beam splitter before reentering the light valves.
The ghost image described above could not, however, be prevented by disposing the quarter-wave phase plate between the projection lens and the polarization beam splitter. That is, in the projection type display device described above, the reflected light beams from the surfaces of the constructive lens elements of the projection lens are not the cause of the ghost image.
As a result of having studied the ghost image that occurred on the projection type display device and pursued the cause thereof, the present inventor has discovered that factors which will hereinafter be mentioned may be principal causes for forming the ghost image.
(1) The light beams, entering the prism member 11A, of the beams of S-polarized light exiting from the S-polarized light outgoing surface of the polarization beam splitter 21 of the projection type display device disclosed in the example of the prior art, partially receive the reflecting action from the incident surface 11a of the prism member 11A, thus travel back, then enter the polarization beam splitter 21, penetrate through a polarization separator, then enter the projection lens, and are projected as the ghost image.
(2) The beams of S-polarized light separated in polarization by the polarization beam splitter 21 are partially reflected by the S-polarized light outgoing surface, thus travel back, then penetrate through the polarization separator, and are projected as the ghost image:
(3) The beams of P-polarized light entering the polarization beam splitter, separated in polarization by the polarization separator and penetrating therethrough, are partially reflected by the P-polarized light outgoing surface, thus travel back, reflected by the polarization separator etc., then travel further, fall upon the projection lens, and are projected as the ghost image.
As explained above, it has proven that the cause of the ghost image is not single, and the ghost image is formed due to a plurality of factors overlapped.
For eliminating those causes, to start with, it might be considered that the reflected light be reduced by forming anti-reflection films on both of the polarization outgoing surfaces of the polarization beam splitter.
Based on this method, however, though capable of reducing the reflected light to some extent, it is impossible to make the reflected light completely disappear. Further, the anti-reflection film is composed of a dielectric multi-layered film, however, with respect to the incident light in a state of linearly polarized light, the penetrating light through and the reflected light from the anti-reflection film are unable to keep their states of being linearly polarized. Therefore, the problem is that both of those beams of light penetrate therethrough or are reflected therefrom as so-called elliptically polarized light having an S (P)-polarized light component in the case of, e.g., an incidence of the P (S)-polarized light.
For example, the reflected light of the P polarization in the item (3) is also reflected as the elliptically polarized light containing the S-component, and hence the S-component among the light beams traveling back is reflected toward the projection lens and inevitably projected as a ghost image.
Furthermore, as to the ghost images relative to the causes explained in the items (1) and (2), it can be considered that the anti-reflection layer is formed on the incident surface of the prism 11A and further formed also on the S-polarized light outgoing surface of the polarization beam splitter. The perfect anti-reflection can not be, as explained above, attained. Besides, those anti-reflection films are used as polarization compensation films for dichroic films utilized for color separations of the light beams to the color light oriented light valves and for color synthesization of the light beams exiting from the light valves and hence there arises a problem of being unable to incorporate a high-performance reflection preventive function. That is, the items (1) and (2) have a more serious problem than in the item (3).
Accordingly, it is a primary object of the present invention, which was devised under such circumstances, to provide a projection type display device capable of preventing unintended reflected light from an outgoing surface, etc. of a polarization beam splitter from entering a projection lens and becoming a cause of a ghost image.
To accomplish the above object, according to a first aspect of the present invention devised to prevent the ghost image due to the above causes from being projected, a projection type display device comprises a color separating/synthesizing optical system for making color separations of light source beams via a polarization beam splitter, light valves disposed for color light, upon which the color-separated light beams are incident, the light beams exiting from the lightvalves being synthesized by the color separating/synthesizing optical system, and the synthesized light beams exiting, a polarization beam splitter for analyzing the synthesized light beams and taking out the analyzed light beams, and a projection lens for projecting the analyzed light beams on a screen. In this projection type display device, a normal line of an outgoing surface of the polarization beam splitter with respect to the light source beams exiting toward the color separating/synthesizing optical system from the polarization beam splitter, has a predetermined angle larger than zero degree with respect to an optical axis of the light source beams, and an incident surface of the color separating/synthesizing optical system with respect to the light source beams exiting toward the color separating/synthesizing optical system from the polarization beam splitter, is disposed in parallel to the outgoing surface of the polarization beam splitter.
In the projection type display device, the normal line of the outgoing surface of the polarization beam splitter has the predetermined angle larger than zero degree with respect to the optical axis of the light source beams. The incident surface of the color separating/synthesizing optical system is disposed in parallel to the outgoing surface of the polarization beam splitter. Therefore, optical paths of the unintended reflected beams of light from the outgoing surface of the polarization beam splitter and from the incident surface of the color separating/synthesizing optical system, can be set off modulated light entering the projection lens, whereby the ghost image can be prevented from being formed.
In the projection type display device according to the first aspect of the invention, the polarization beam splitter includes a plurality of optical prism members, and the following formula is satisfied:
sin(2xcex8) greater than 2xc2x7NA/nxc2x7(1xe2x88x92NA2)xc2xd
where xcex8 is the predetermined angle made by the normal line of the outgoing surface of the polarization beam splitter and by the optical axis of the light source beams, n is the refractive index of each of the optical prism members constituting the polarization beam splitter, and NA is the numerical aperture of the projection lens on the side of the light valve.
In the projection type display device according to the first aspect of the invention, the optical axis of the light source beams entering the polarization beam splitter has an incident angle of 45 degrees to a polarization separator of the polarization beam splitter. The polarization beam splitter includes two triangular prisms, wherein one triangular prism has three apex angles of which one is 45 degrees, another is an obtuse angle, and the remaining is an acute angle, and the other triangular prism has three apex angles of which one is 45 degrees. A surface interposed between the apex angle of 45 degrees and the acute angle of one triangular prism and a surface including the apex angle of 45 degrees of the other triangular prism, are bonded in a state where the apex angles of 45 degrees are matched with each other and a polarization separation film is interposed therebetween.
In the projection type display device according to the first aspect of the invention, the optical axis of the light source beams entering the polarization beam splitter has an incident angle xcex1 other than 45 degrees to a polarization separator of the polarization beam splitter. The polarization beam splitter includes two. triangular prisms, wherein one triangular prism has three apex angles of which one is xcex1 degrees, another is (xcex1+xcex8) degrees if the predetermined angle is set to xcex8, and the other triangular prism has three apex angles of which one is xcex1 degrees. A surface interposed between the apex angle xcex1 and the apex angle (xcex1+xcex8) of one triangular prism and a surface including the apex angle xcex1 of the other triangular prism, are bonded in a state where the apex angles xcex1 are matched with each other and a polarization separation film is interposed therebetween.
According to a second aspect of the present invention, a projection type display device comprises a color separating/synthesizing optical system for making color separations of light source beams via a polarization beam splitter, light valves, disposed for color light, upon which the color-separated light beams are incident, the light beams exiting from the light valves being synthesized by the color separating/synthesizing optical system, and the synthesized light beams exiting, a polarization beam splitter for analyzing the synthesized light beams and taking out the analyzed light beams, and a projection lens for projecting the analyzed light beams on a screen. In this projection type display device, the light beams among the light source beams, which are reflected by an outgoing surface of the polarization beam splitter, exit from the polarization beam splitter via the polarization separator of the polarization beam splitter and enter the projection lens, do not pass through an aperture defined by an aperture stop of the projection lens.
According to a third aspect of the present invention, a projection type display device comprises a color separating/synthesizing optical system for making color separations of light source beams via a polarization beam splitter, light valves, disposed for color light, upon which the color-separated light beams are incident, the light beams exiting from the light valves being synthesized by the color separating/synthesizing optical system, and the synthesized light beams exiting, a polarization beam splitter for analyzing the synthesized light beams and taking out the analyzed light beams, and a projection lens for projecting the analyzed light beams on a screen. In this projection type display device, the light beams among the light source beams, which exit from the polarization beam splitter, then are reflected directly from an incident surface of the color separating/synthesizing optical system and enter the projection lens via the polarization beam splitter, do not pass through an aperture defined by an aperture stop of the projection lens.
In the projection type display device according to the second aspect of the invention, the following construction may be adopted, wherein the light beams among the light source beams, which exit from the polarization beam splitter, then are reflected directly from an incident surface of the color separating/synthesizing optical system and enter the projection lens via the polarization beam splitter, do not pass through an aperture defined by an aperture stop of the projection lens.
According to a fourth aspect of the present invention, a projection type display device comprises a color separating/synthesizing optical system for making color separations of light source beams via a polarization beam splitter, light valves, disposed for color light, upon which the color-separated light beams are incident, the light beams exiting from the light valves being synthesized by the color separating/synthesizing optical system, and the synthesized light beams exiting, a polarization beam splitter for analyzing the synthesized light beams and taking out the analyzed light beams, and a projection lens for projecting the analyzed light beams on a screen. In this projection type display device, the other beams of polarized light among the light source beams, which are separated in polarization by the polarization beam splitter, then are reflected by an outgoing surface of the polarization beam splitter, exit from the polarization beam splitter via a polarization separator of the polarization beam splitter and enter the projection lens, do not pass through an aperture defined by an aperture stop of the projection lens.
According to a fifth aspect of the present invention, a projection type display device comprises a color separating/synthesizing optical system for making color separations of light source beams via a polarization beam splitter, light valves, disposed for color light, upon which the color-separated light beams are incident, the light beams exiting from the light valves being synthesized by the color separating/synthesizing optical system, and the synthesized light beams exiting, a polarization beam splitter for analyzing the synthesized light beams and taking out the analyzed light beams, and a projection lens for projecting the analyzed light beams on a screen. In this projection type display device, a normal line of an outgoing surface of the polarization beam splitter with respect to the light source beams exiting toward the color separating/synthesizing optical system from the polarization beam splitter, has a predetermined angle larger than zero degree with respect to an optical axis of the light source beams.